The proposed project has three aims. First, it will test the feasibility and acceptability of a conditional economic incentives (CEI) program to incentivize self-protection and health-care-seeking behaviors among male sex workers (MSW) in Mexico City. The working hypothesis is that a program with modest economic incentives to stay free of sexually transmitted infections (STI) can be implemented among MSW to incentivize condom use and reduction of sex partners. We hypothesize that CEI treatment groups will exhibit greater program participation and retention rates as compared to the control group. Second, it will obtain estimates of the effect of CEI on primary outcomes: reported condom use and reported number of sexual partners. Our working hypothesis is that there will be a dose-response effect where participants with progressively higher CEI will show more protective behaviors than the controls. We hypothesize that higher levels of CEI will be associated with higher rates of reported condom use and greater reductions in the number of sex partners. Third, it will examine the degree to which CEI impact secondary outcomes: incident cases of STI, and prices for commercial sex transactions. The working hypothesis is that the CEI treatment groups will have reduced rates of STI and they will face lower prices for commercial sex transactions. This pilot trial will include MSW only, ages 18-25, recruited from community sites in Mexico City (n=300). After completing baseline measures, all participants will take part in a standard single-session information/prevention workshop (on the benefits of condom use for HIV/STI prevention, and condom negotiation). They will then be randomized into 1 of 3 groups: control, treatment 1 and treatment 2. In Treatment 1 (100 individuals) receive low incentive ($200 pesos/each time) only if they are free of STIs at months 6 and 12. Treatment 2 (100 individuals) receive high incentive ($500 pesos/each time) only if they are free of STIs at months 6 and 12. Controls (100 individuals) will not receive any CEI even if they are free of STIs at months 6 and 12. However, everyone will receive inconvenience fee ($70 pesos/each time at baseline, month 6 and month 12). There will be 15-20 min. reinforcing sessions for everyone at months 6 and 12 when receiving STI results, and CEI for those in either treatment group. STI testing and counseling will be conducted at Clinica Condesa (largest HIV clinic in Mexico City) in collaboration with the Mexican School of Public Health/National Institute of Public Health (INSP) through the Consortium of HIV Research (CISIDAT), and Brown University. PUBLIC HEALTH RELEVANCE: The overall objective of the current application is to implement a pilot project offering conditional economic incentives (CEI) for HIV/STI prevention among male sex workers (MSW) in Mexico City, to test feasibility and acceptability, and to gather preliminary evidence on effects sizes to inform a future efficacy trial. CEI are an innovative structural approach for HIV prevention, which so far has not been tested in concentrated epidemic settings.